Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220829151536.8578-1-jandryuk@gmail.com> <31F127F6-A096-4991-9D4C-1B2E032689A1@gmail.com>
In-Reply-To: <31F127F6-A096-4991-9D4C-1B2E032689A1@gmail.com>
From:   Jason Andryuk <jandryuk@gmail.com>
Date:   Thu, 1 Sep 2022 08:55:41 -0400
Message-ID: <CAKf6xpvZNHQyQq9zqNpD0kXFK+pryAKKbRDxoiMkB=PrhvSGKQ@mail.gmail.com>
Subject: Re: [PATCH] xen-pcifront: Handle missed Connected state
To:     Rich Persaud <persaur@gmail.com>
Cc:     Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        Oleksandr Tyshchenko <Oleksandr_Tyshchenko@epam.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        xen-devel <xen-devel@lists.xenproject.org>,
        linux-pci@vger.kernel.org, open list <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Wed, Aug 31, 2022 at 10:35 PM Rich Persaud <persaur@gmail.com> wrote:
>
> On Aug 29, 2022, at 11:16 AM, Jason Andryuk <jandryuk@gmail.com> wrote:
> >
> > =EF=BB=BFAn HVM guest with linux stubdom and 2 PCI devices failed to st=
art as
> > libxl timed out waiting for the PCI devices to be added.  It happens
> > intermittently but with some regularity.  libxl wrote the two xenstore
> > entries for the devices, but then timed out waiting for backend state 4
> > (Connected) - the state stayed at 7 (Reconfiguring).  (PCI passthrough
> > to an HVM with stubdomain is PV passthrough to the stubdomain and then
> > HVM passthrough with the QEMU inside the stubdomain.)
> >
> > The stubdom kernel never printed "pcifront pci-0: Installing PCI
> > frontend", so it seems to have missed state 4 which would have
> > called pcifront_try_connect -> pcifront_connect_and_init_dma
>
> Is there a state machine doc/flowchart for LibXL and Xen PCI device passt=
hrough to Linux? This would be a valuable addition to Xen's developer docs,=
 even as a whiteboard photo in this thread.

I am not aware of one.

-Jason